Various exposure apparatuses have been employed when semiconductor elements, thin film magnetic heads, or liquid crystal display elements are manufactured using photolithographic processes, however, in general, an apparatus is used which projects a pattern image formed on a photomask or reticle (hereinafter referred to as a “reticle”) onto a substrate such as a wafer or a glass plate (hereinafter referred to as a “wafer”), the surface of which has applied thereon a sensitizer such as a photoresist, via a projection optical system. In such an exposure apparatus, a highly accurate temperature control is required in order to carry out exposure processes for minute patterns, and a high level of cleanliness must be maintained by decreasing contaminants in the apparatus. For these reasons, an exposure apparatus is placed in a chamber and the temperature in the chamber is controlled by using an air-conditioning system. Also, the cleanliness of the chamber is maintained by providing a filter for removing contaminants at a part of the flow path of the air-conditioning system.
The chamber used for accommodating the exposure apparatus is divided into a plurality of air-conditioning chambers including an exposure chamber in which the body of the exposure apparatus is accommodated, a reticle loader chamber in which a reticle loader system for loading and unloading a reticle relative to the body of the exposure apparatus is accommodated, and a wafer loader chamber in which a wafer loader system for loading and unloading a wafer relative to the body of the exposure apparatus is accommodated. In addition, the exposure chamber is made of an air-conditioning chamber in which a part thereof, i.e., a main column for accommodating a wafer stage is separated. Also, the air-conditioning system includes an overall air-conditioning system for carrying out an overall air-conditioning for the exposure chamber, and a local air-conditioning system for carrying out a local air-conditioning for each of the main column, the reticle-loader chamber, and the wafer loader chamber.
Here, in the local air-conditioning system for the main column and the wafer loader chamber, the air-conditioning is carried out using a chemical filter which removes substances that enhance resist deterioration, such as ammonia, in order to protect the resist applied to the wafer. In the overall air-conditioning system for the exposure chamber, on the other hand, labor for maintenance and running cost will increase if a chemical filter is used since a large amount of air is required for the overall air-conditioning system and hence the chemical filter is quickly contaminated and needs to be frequently replaced. Accordingly, the air-conditioning is carried out without using a chemical filter in the overall air-conditioning system. Thus, if a gas flows into the main column or the wafer loader chamber in which the air-conditioning is performed using a chemical filter, from the exposure chamber in which the air-conditioning is carried out without using a chemical filter, problems such as increase in resist deterioration of the wafer may be caused.
Also, if contaminants are present in an optical path space, which is a space through which the exposure light passes, problems may be caused in that an exposure process cannot be performed with high accuracy due to factors such as the exposure light being attenuated and cannot reach the wafer with a sufficient strength, or unevenness of illuminance occurs on the wafer.
Conventionally, attempts have been made to prevent the flow of gas that is present outside the chamber into the inside of the chamber by increasing the pressure inside the chamber that accommodates the entire exposure apparatus to be positive all the time with respect to the pressure outside the chamber. However, since the difference in pressure between each of the air-conditioning chambers inside the chamber is very small, a large difference in pressure may be caused and a gas flow (air current) may be generated among each of the air-conditioning chambers and an appropriate air-conditioning cannot be performed unless the pressures are accurately controlled. In the above case, if a flow is generated in the main column, for example, a large change (fluctuation) in the gas refractive index is locally caused. Accordingly, problems may be generated so that it is not possible to achieve an exposure process with high accuracy and so that the accuracy in measurement of optical measuring devices (a laser interferometer, etc.) is reduced. Also, it becomes evident that an accurate pressure control is essential for each exposure apparatus because the differences in pressures are very small as mentioned above and influence due to the differences among the exposure apparatus (i.e., minute errors, etc., generated during the production of the main body of the exposure apparatus, chambers, and so forth).
As explained above, although there is a danger that the resist of the wafers may be deteriorated, the cleanliness of the optical path space for the exposure light cannot be maintained to a predetermined level, and a flow is caused among the air-conditioning chambers and a stable exposure process cannot be achieved, unless the pressure is accurately controlled inside the chamber having a plurality of air-conditioning chambers, a strict pressure control is not conventionally carried out.